In analyzing the biological function data, it is often attempted to totally diagnose a plurality of function data. In the analysis of cerebral perfusion function data, for example, the diagnosis is carried out, usually, by totally observing the data obtained from a plurality of functional images such as cerebral blood flow (CBF) image, cerebral blood volume (CBV) image, mean transit time (MTT) image, as well as data (e.g., early CT sign and anatomical impression such as running of blood vessels, positions of tissues, etc.) obtained from a tomogram.
An image display method for displaying biological function data has been disclosed in JP-A-2002-282248 wherein a piece of functional image is superposed on a tomogram and is displayed as apiece of composite image. According to this method, the data obtained from the tomogram and the data obtained from a functional image are displayed on a piece of image. A range of measurement is divided into a plurality of sections for each parameter of blood flow, blood volume and mean transit time, and different hues are allocated to the sections of measurement by using a color map. However, since only one parameter is displayed, it is difficult to totally recognize whether the biological function abnormality, symptom and danger are of light degrees or serious degrees (hereinafter referred to as danger degree). Besides, since color is displayed on the whole tomogram, the data are so complex that the abnormality cannot be easily judged.
As a method of observation by displaying a plurality of functional images obtained through examinations of a plurality of number of times, there has been proposed a method called SISCOM (subtracted ictal SPECT co-registered to MRI) by subtracting the SPECT (single photon emission computed tomography) images and composing a region where a distinct change is appearing on a standard brain MR image. This method is to obtain a functional image by subtracting SPECT images obtained, particularly, from an epileptic person during the ictal moment and the interictal moment. Here, an electrode-type electroencephalogram (EEG) is also used in combination. The above SISCOM is corresponding to the SPECT image only, but cannot be applied to the functional images formed from a CT image or an MR image. That is, when the tomograms obtained by different image diagnostic devices are overlapped one upon the other, unlike when the tomogram is obtained using a single image diagnostic device, it is necessary to transform the CT image or the MR image into a standard brain. However, it is difficult to bring the positions and the shapes into agreement. Besides, both the SPECT image and the MR image must be obtained, and the patient must be held locked for extended periods of time. Further, when the SPECT image and MR image are to be overlapped one upon the other, the SPECT image is deformed to meet the standard brain and is adjusted for its position with the MR image imposing a probability of losing the inherent shape of the patient's brain and of losing important data related to the shape. When the patient's skull is deformed, in particular, the loss of data of the shape becomes a serious problem.